Imagine requesting a ride by using your smartphone. Within a few minutes, a sleek, environmentally friendly car pulls up and the ride is automatically charged to your credit card, with tip included.

If the Facebook advertisements are true, Portland may soon get all that from Uber, the ride-sharing service that has sparked protests by taxi companies in some cities.

In the past week, Facebook users have noticed ads recruiting Uber drivers for the Portland area. The ads include links to application and background check forms.

“Uber, are the Facebook ads true? Are you recruiting UberX drivers in Portland, Maine?” Adam B. Zimmerman, a Portland-based lawyer, said on Twitter. “We are so ready for you out here.”

Uber is a private service that connects riders to drivers through a smartphone app with pre-registered credit cards. Trips are reserved and paid for through the mobile app, and a user can track the location of the car as it makes its way to the pickup point. The service has price options including luxury, SUV and uberX, the lower-cost version.

Kaitlin Durkosh, a spokeswoman for Uber, said the San Francisco-based startup often tests ads to gauge the feasibility of service in various markets.

“So far, we’ve received overwhelmingly positive support from residents and visitors in the city looking for transportation alternatives like Uber, and interest from potential driver partners looking for economic opportunities,” Durkosh said in an email. “We are excited about the potential opportunity to connect riders and drivers in Portland.”

Uber now operates in 140 cities worldwide, including New York, Boston and Providence, Rhode Island, and is expanding to several new cities each week.

Since April, it has starting launching in smaller cities, with populations of less than 60,000, including Chapel Hill, North Carolina, Fairfield, Connecticut, and Palm Springs, California.

“Uber aspires to be in every city around the world where current transportation options fall short of meeting consumer and driver demand,” Durkosh said. “We are always exploring which city will be next.”

As a tech company, Durkosh said, Uber can track when riders download and open the app, so it can tell when there is a demand in certain cities.

The demand for such service often comes at the expense of the local taxi industry.

Taxi cabs and drivers need commercial licensing that is regulated by local officials. But most cities lack appropriate language to regulate ride-sharing services, so those services aren’t restricted by the same rules as taxis and can offer more choices and lower prices.

In Washington, D.C., and London, the Uber service has led to protests and strikes among taxi drivers, who have demanded equal treatment.

Jessica Grondin, a spokeswoman for Portland, said that if Uber launched in the city, it could potentially fall under the city’s livery regulations, which regulate limousines and other for-hire cars.

According to Portland’s city code, drivers who charge fees to pick up and drop off passengers at predetermined locations must have licenses and extensive background checks to operate. Grondin said it would take further legal consideration to determine whether the regulation would cover Uber.

Taxis in Portland charge $1.90 for the first one-tenth of a mile and 30 cents for each additional tenth of a mile. They cover Portland, South Portland, Westbrook, Cape Elizabeth, Falmouth and Scarborough.

While Uber has no time line for a Maine launch, some taxi drivers in Portland generally think it’s a good idea.

“I’d use it,” said Daniel Robinson, a driver for Elite Cabs who has worked as a driver for eight years. “A lot of cab drivers, when they aren’t working, need cabs too.”

While Robinson hadn’t heard of Uber, he said he thinks there is enough demand for cabs in Portland that it wouldn’t hurt his business.

Musa Khater, who has been working as a cab driver in Portland for a year and a half, agreed.

“I’m not a cab company so it’s good for me,” Khater said while waiting in front of DiMillo’s on the Water restaurant on Commercial Street.

Khater said he had been waiting for almost an hour for someone to hail his cab. With Uber, he said, it would be easier to dispatch drivers to the places where cars are most needed.

“I’ve got a life, bills to pay and a family to take care of, and if (Uber) comes here and adds something to the Maine people, it’s good,” Khater said. “But if not, it won’t be so good.”

Uber’s Facebook ads have received a positive response from social media users in the Portland area.

“That would be awesome,” Zimmerman, the Portland lawyer, said in a phone interview. “I’ve used Uber in at least five different cities and would be using it a lot if it came to Portland.”